Adding landing page content from https://docs.google.com/document/d/1aMWe0plrR9A9v0EM64O0lj1O7iTYM3GSLVW2dnYWL0Y/edit#.

Also added share buttons from http://www.sharethis.com. Test please.

Updated links. Set to open new window.
Merged in David's changes
Change twitter/facebook share URL to include 'mesh'
Merge branch 'meshrdf' into meshrdf-klortho
Changed headings, added (beta), changed link to SPARQL
Revised headings.
Added (beta) to twitter.
Revised link to SPARQL endpoint.
Merge pull request #13 from HHS/meshrdf-david

Meshrdf david
change namespace and sample query